1. Field of the Invention
The present invention relates to an ophthalmic apparatus used at, for example, an eye clinic for picking up an image of a fundus of a subject's eye.
2. Description of the Related Art
In conventional ophthalmic apparatuses, an optical system that is separate from an image-pickup optical system is provided for the purpose of facilitating the positioning between the apparatus and the subject's eye. A target member, which serves as a fixation target, is disposed within that optical system at a position where the target member is in a conjugate relationship with the fundus of the subject's eye. The target member is illuminated from the back so that the target thereof can be projected onto the fundus of the subject's eye.
Japanese Patent Laid-Open No. 10-192244 discloses an ophthalmic apparatus which includes an optical member and an anterior-ocular-observation optical system disposed in a removable manner. The optical member has a scattering-reflecting area, serving as a fixation target for anterior-ocular observation, in at least one section of a surface thereof that is distant from the subject's eye. The anterior-ocular-observation optical system has a light source configured to illuminate the optical member from the side.
Japanese Patent Laid-Open No. 11-225970 discloses an improved version of the ophthalmic apparatus of Japanese Patent Laid-Open No. 10-192244. In detail, this ophthalmic apparatus includes a fixation target member for anterior-ocular-observation formed by using a luminous coating material, a switching unit configured to move the fixation target member onto a light path or to remove the fixation target member from the light path, and an illuminating unit configured to illuminate the fixation target member when the fixation target member is removed from the light path.
In the ophthalmic apparatus according to Japanese Patent Laid-Open No. 11-225970, in order to simplify the structure of the apparatus, the optical member having its scattering-reflecting area set on a fundus-conjugate plane of an observation/image-pickup optical system at the time of anterior-ocular observation is disposed in a removable manner together with a lens group used for anterior-ocular observation. By illuminating the optical member from the side, the light from the scattering-reflecting area can be projected onto the subject's eye as a fixation target. In this apparatus, the optical member having the scattering-reflecting area is provided within the anterior-ocular-observation lens group and is used as a fixation target member for anterior-ocular observation.
However, in the conventional examples described above, when the anterior-ocular-observation lens group is removed from the light path to switch from an anterior-ocular observation mode to a fundus observation mode, the position of the fixation target for anterior-ocular-observation projected on the subject's eye differs from the position of the fixation target for fundus observation projected on the subject's eye. This implies that the visual line direction of the subject's eye changes in response to the switching operation. Therefore, even if the positioning between the subject's eye and the apparatus is adjusted for the anterior-ocular observation mode, the positioning process will need to be performed again for the fundus observation mode.
Normally, for a screening test, such as a mass health examination, a fundus image in which the optic disc and the macula lutea are evenly disposed is captured. For this reason, if the visual line changes upon switching to the fundus observation mode, the fixation of the subject's eye needs to be guided again, thus leading to a troublesome and complex operation. In addition, if the fixation target for fundus observation is preliminarily disposed at a position suitable for a certain kind of examination, the subject may possibly lose sight of the fixation target since the fixation target will suddenly be switched to another one upon switching from the anterior-ocular observation mode to the fundus observation mode.
The present invention provides an ophthalmic apparatus that prevents the subject from losing sight of a fixation target even in the case of switching between the anterior-ocular observation mode and the fundus observation mode.